1. Technical Field
The present invention relates to a liquid discharge apparatus (liquid ejecting apparatus) that applies a drive signal to an actuator and discharges (ejects) a liquid, and for example, is suitable for a liquid ejecting type printing apparatus that is made so as to print a predetermined character, an image or the like, by ejecting a minute liquid from a nozzle of a liquid ejecting head and forming a fine particle (dot) on a printing medium.
2. Related Art
In a liquid ejecting type printing apparatus, in order to eject a liquid from a nozzle of a liquid ejecting head, an actuator such as a piezoelectric element is arranged, and it is necessary to apply a predetermined drive signal to the actuator. Since the drive signal has relatively a high potential, it is necessary to power-amplify an original signal which is a reference of the drive signal, with a power amplification circuit. Therefore, in JP-A-2011-5733, in comparison with an analog power amplifier, using a digital power amplification circuit of which a power loss is very small and a size can be miniaturized, the original signal is made as a modulation signal by pulse-modulating with a modulation circuit, the modulation signal is made as a power amplification modulation signal by power-amplifying with the digital power amplification circuit, and the power amplification modulation signal is made as a drive signal by smoothing with a smoothing filter. In the drive signal, or the original signal to be the reference thereof, there is a portion (time) where the potential does not change, but the piezoelectric element which is used as an actuator is a capacitive load, and it is not necessary to supply a current to the actuator when the potential of the drive signal does not change. Therefore, in the liquid ejecting type printing apparatus which is described in JP-A-2011-5733, when the potential of the actuator is maintained to be constant, that is, when the potential of the original signal is maintained to be constant, an operation is stopped by turning off a high side switching element Q1 in company with a low side switching element Q2 which are installed in the digital power amplification circuit, and thereby reducing power consumption in the digital power amplification circuit and the smoothing filter.
Incidentally, in JP-A-2011-5733, the low side switching element Q2 may operate using a ground potential as a reference, but the high side switching element Q1 is necessary to operate using the potential of an output node (connection node with the low side switching element Q2) as a reference. Therefore, it is not shown in JP-A-2011-5733, a bootstrap capacitor functioning as a floating power supply, is connected between an external power supply and the output node of the digital power amplification circuit. Furthermore, since the output node becomes the high potential when the high side switching element Q1 is turned on, so that the current does not flow backward to the external power supply side from the output node, a diode for backflow prevention is arranged between the external power supply and the bootstrap capacitor.
In the digital power amplification circuit of the related art described above, when the low side switching element Q2 is turned on, the current flows to the ground through the diode from the external power supply, and the bootstrap capacitor is charged. In particular, in a state where the external power supply starts, when the low side switching element Q2 is firstly turned on, a large current flows to the ground in a moment from the external power supply. Therefore, if a portion of the large current flows to the piezoelectric element which is used as an actuator through the smoothing filter, there is a concern that the liquid is discharged from the nozzle by mistake, or the piezoelectric element is damaged. Moreover, due to the large current, an output voltage of the external power supply is largely reduced in a moment, and a large reverse direction current (reverse current) to which a reverse bias is applied, flows, before a forward direction current of the diode becomes 0. Therefore, so that the diode is not damaged due to heat generation, it is necessary to use a diode having a large current resistant amount, a fast recovery diode, or the like, and it becomes a factor of a cost increase.